Hydride Dynamics in Triosmium and Triruthenium Carbonyl Clusters: Synthesis, Reactivity and Dynamics of a Trihydrido Quinoline-4-Carboxaldehyde Triosmium Cluster

Abstract

An overview of the dynamical processes involving the hydrido ligand in triosmium and triruthenium carbonyl clusters is presented. The relationship between the mechanisms of hydride motions and the other ligands in the cluster are discussed for mono- di- and trihydrido-clusters. In addition, the reactivity of the electron deficient 46e− cluster, (μ-H)(μ3-η2-C9H5N-4-CHO)Os3(CO)9 (1) with hydrogen is reported. The reaction gives two isomeric trihydrido clusters, H(μ-H)2(μ3-η2-C9H5N-4-CHO)Os3(CO)8 (2) and (μ-H)3(μ3-η2-C9H5N-4-CHO)Os3(CO)8 (2′) in low yield along with trace amounts of other hydrido clusters. Reaction of the inseparable mixture of 2 and 2′ with triphenylphosphine at ambient temperatures gives two related addition products H(μ-H)2(μ-η2-C9H5N-4-CHO)Os3(CO)8PPh3 (3) and (μ-H)3(μ-η2-C9H5N-4-CHO)Os3(CO)8PPh3 (3′) in a 5:1 ratio. These results contrast with the previously reported trihydrido-derivatives of triosmium μ3-η2-imidoyl clusters where only analogues of 2 and 3 are obtained. Clusters 2 and 2′ are rigid on the NMR time scale while 3 exhibits dynamical behavior in the temperature range of −50 to +25 °C. Cluster 3′ is stereochemically rigid in this temperature range. The dynamical behavior of 3 involves the exchange of the terminal and bridging hydrides coupled with tripodal motion of the phosphine substituted osmium atom, a process virtually identical to previously reported trihydrides of the μ3-η2-imidoyl triosmium clusters.